Non-invasive methods for assessment of body composition.
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Adipose Tissue↗
Biomedical subjects
C H Knight
Publications and source records attributed to C H Knight.
Exogenous GnRH induces ovulation in seasonally anoestrous lactating goats (Capra hircus).
A specific sheep LH radioimmunoassay was validated for the measurement of goat LH, and used to monitor luteal-phase LH episodes and the preavulatory LH surge in progestagen sponge-synchronized cycling goats. No luteal-phase LH episodes were detected during 12 h of frequent (15-min) blood sampling in 2 goats. A preovulatory LH surge was recorded in 5/5 goats, with a mean amplitude of 45.4 +/- 7.2 ng/ml and a mean time of onset of 38.4 +/- 1.2 h after removal of a progestagen-impregnated sponge. In anoestrous goats, single i.v. injections of 1000 and 2000 ng GnRH induced LH episodes with a mean amplitude of 2.04 +/- 0.11 and 3.67 +/- 0.06 ng/ml respectively, but injections of 250 or 500 ng did not consistently elevate LH concentrations. Progestagen-primed, seasonally anoestrous lactating goats were treated with repeated injections of 1500 ng GnRH (every 2 h for 52 or 78 h) in May 1985 or 1986. All 10 had kidded in March of the same year, and were consequently at peak lactation at the time of GnRH treatment. A preovulatory LH surge was detected in 9 goats with a mean time of onset of 59.5 +/- 2.9 h (1985) or 39.6 +/- 3.3 h (1986) after vaginal sponge removal. All animals displayed oestrus and ovulated, and 9 of the goats were mated: in 5 of these animals pregnancies were successfully carried to term. The results show episodic LH release in response to GnRH and indicate that ovulation can be induced in seasonally anoestrous goats, even at peak lactation, and normal pregnancies may result.
Anestrus↗
Autocrine regulation of casein turnover in goat mammary explants.
Local feedback control of milk protein secretion was investigated in goat mammary explants by measuring degradation of newly synthesized casein in the presence of a goat milk whey fraction. Reduced net synthesis of [3H]casein in the presence of the milk fraction was due, at least in part, to its degradation during secretion, suggesting that this process is under autocrine regulation.
Animals↗
Metabolic adaptations in mouse mammary gland during a normal lactation cycle and in extended lactation.
The development and involution of mouse mammary tissue was measured in terms of changes in the cell population and the synthetic capacity of cells during the course of pregnancy, lactation and natural weaning, and after lactation was extended by introduction of foster litters of younger pups. Synthetic capacity was assessed by measuring the activities of several key enzymes closely concerned with the synthesis of milk constituents together with other constitutive enzymes. The capacity of the tissue to synthesize lactose and casein was also measured using short-term cultures of freshly prepared mammary explants. Results showed that the mammary cell population began to increase and differentiate around the time of parturition. Cell numbers increased up to day 5 of lactation, whereas cellular differentiation continued through lactation until day 15, around the time of peak milk yield. After day 15 there was a sharp drop, followed by a gradual decline in synthetic capacity and cell population, as pups were weaned. Substitution of younger pups for the natural litter at day 15 prevented the normal fall in milk secretion. In this case, mammary cell number remained at day 15 levels; cellular differentiation was also maintained to a considerable degree, although several markers of differentiation decreased during extended lactation.
Adaptation, Physiological↗
Compensatory changes in mammary development and function after hemimastectomy in lactating goats.
Goats were hemimastectomized during Weeks 5 or 8 of lactation. The milk yield of the remaining gland (the test gland) usually increased in a compensatory fashion after the operation, although the degree of response varied from no response to a 50% increase. The glands of those goats that responded and received no further treatment maintained an increased milk yield for the duration of the lactation. Changes in the size and composition of the gland were investigated by a combination of udder volume and biopsy in some goats. Increases in both gross size and total DNA content (DNAt, a measure of cell number) were observed in all of these, although the timing of the response varied between individuals. Overall, cell population size was maintained for at least 18 weeks after hemimastectomy whereas in control (unoperated) goats DNAt decreased by 35% over a similar period.
Animals↗
Effects of long-term thrice-daily milking on mammary enzyme activity, cell population and milk yield in the goat.
In two separate experiments, lactating goats were milked unilaterally thrice daily instead of twice daily for periods of 13 and 37 wk, starting at 2 to 5 wk after parturition. The other gland was milked twice daily throughout. In both experiments thrice-daily milking increased milk yield significantly. In the first experiment, after 37 wk the amounts of RNA and DNA, rate of cell proliferation and activities of several enzymes per cell were greater in the thrice-milked gland (P less than .05). In the second experiment, after 9 or 10 d of thrice-daily milking the activities of several key mammary enzymes per cell measured in biopsy samples had increased in the thrice-milked but not the twice-milked gland. After 13 wk of thrice-daily milking, the DNA content of the glands and the activity per cell of the key enzymes was the same in both glands, showing that the synthetic capacity of the gland was being used more effectively in the treated gland. These results indicate that several mechanisms contributed to the increased milk yield induced by thrice-daily milking.
Animals↗
Mammary growth during lactation: implications for increasing milk yield.
Milk yield is greatly influenced by the size of the mammary secretory cell population. In rats, proliferation of cells during early lactation may account for as much as three-quarters of the increase in daily milk yield between parturition and peak lactation; the remainder is due to increased activity of existing cells. Conversely, in goats, all the initial decline in milk yield after peak lactation can be attributed to loss of secretory cells. Increased frequency of milking enhances milk yield and reduces secretory cell loss, whereas goats hemimastectomized at peak lactation undergo compensatory changes in the remaining gland, which include a complete maintenance of cell number for at least 18 wk. Cell proliferation is increased in both cases, showing that mammary growth can occur during established lactation. The significance of this observation is discussed in relation to ways in which the milk yield of dairy animals might be increased.
Animals↗
Milk yield and composition in mice: effects of litter size and lactation number.
Milk yield was measured by a tritiated water dilution procedure during consecutive lactations in mice suckling four, 10 or 18 young. Analysis of variance revealed positive effects of lactation number and litter size on milk yield. There was a significant correlation between maternal body weight and parity; increased body weight accounted for some, but not all, of the parity-related increases in milk yield. Peak milk yield was reached between days 10 and 16 of lactation, but the efficiency with which the growing young utilized milk for weight gain was greatest before day 7. Milk composition varied significantly during the course of lactation.
Animals↗
Degradation of newly-synthesised casein in mammary explants from pregnant and lactating goats.
Casein degradation was measured by a pulse-chase method in explants from freshly-prepared from goat mammary tissue. An initial increase in L-[5-3H]proline radioactivity incorporated in casein during the chase period was followed in some conditions by a decrease resulting from intracellular degradation of the major casein polypeptides. Differences in the proportion of casein degraded in explants cultured with or without prolactin suggested that the process was under hormonal control. Greater degradation of casein by explants obtained in late pregnancy and early lactation suggested that the process may affect net casein production in vivo.
Animals↗
Metabolic adaptations in goat mammary tissue during pregnancy and lactation.
Metabolic adaptations of goat mammary tissue during pregnancy and lactation were monitored in serial biopsies of the tissue. Changes in the synthetic capacity of secretory cells were studied by combining measurements of enzyme activities with short-term culture of mammary explants to measure lactose, casein and total protein synthesis. By these criteria, the main phase of mammary differentiation began in late pregnancy and was essentially complete by Week 5 of lactation, coinciding with the achievement of peak milk yield. While milk yield declined after Week 5, the activities of key enzymes expressed per mg DNA and the rates of lactose and casein synthesis in mammary explants were maintained over a considerable period. The results suggest that changes in the synthetic capacity of epithelial cells may account for much of the rise in milk yield in early lactation, but are not responsible for the declining phase of milk production characteristic of lactation in ruminants.
Acetyl-CoA Carboxylase↗
Inhibitory effects of bromocriptine on mammary development and function in lactating mice.
Five experiments were conducted. In the first, the plasma prolactin concentration of lactating mice was significantly reduced 3, 6 and 12 h after a single injection of 0.2 mg bromocriptine at 09.00 h, but recovered to normal levels at 24 h. A second injection at 17.00 h (i.e. total dose of 0.4 mg) completely prevented this recovery. Prolactin concentration was also reduced after the s.c. implantation of a solid pellet of bromocriptine. Once daily injections of bromocriptine for 7 days starting 1-day prepartum (early lactation group) or on day 5 of lactation (established lactation group) significantly reduced milk yield, assessed from the weight gain of the litter or estimated by a tritiated water dilution procedure. In early lactation the degree of inhibition was positively related to the size of the suckling litter (three pups, no inhibition; nine pups, 16.4% inhibition; 14 pups, 40.8% inhibition), but in established lactation an inhibition of 25-30% was observed, regardless of litter size. Twice-daily injections and s.c. implants of bromocriptine both reduced milk yield by a greater amount (approximately 45%), but in no case was secretion completely suppressed. The inhibitory effect of bromocriptine was prevented by the simultaneous administration of ovine prolactin (0.4 mg). Lactogenesis was apparently not affected by bromocriptine treatment. At the end of the early lactation treatment period, the mammary glands of bromocriptine-treated animals were significantly smaller and contained fewer cells than those of controls, but this was not the case in animals treated during established lactation.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Effects of an antiserum to rat growth hormone on lactation in the rat.
A highly specific antiserum to rat GH (anti-rGH) was used to assess the role of GH in lactation in the rat. When administered alone, anti-rGH had no effect on litter weight gain, whereas bromocriptine reduced serum prolactin concentrations and litter weight gain for up to 7 days when given on day 4 of lactation. When bromocriptine and anti-rGH were given in combination, however, litter weight gain declined even more dramatically so that pups were receiving virtually no milk 2-3 days after treatment. Daily litter exchange failed to prevent this effect. Concurrent injections of highly purified GH (prolactin contamination undetectable) prevented the dramatic decline in litter weight gain induced by combined bromocriptine and anti-rGH treatment, so that these litters grew as well as those receiving bromocriptine alone. Growth hormone did not act by influencing serum prolactin concentrations, which remained low during GH therapy. Direct effects of anti-rGH or GH on the pups (transferred through the milk) were ruled out since virtually identical results were obtained when milk yield was estimated during a 30-min suckling period after a 3-h separation of mother and pups. Lactation had virtually ceased 3 days after treatment with both bromocriptine and anti-rGH, but it could be reinitiated by a single injection of prolactin or GH, and subsequent recovery was virtually complete. The results of this study show that prolactin can maintain a full milk yield in the absence of GH, milk yield is reduced by approximately 50% in the absence of prolactin and milk yield is totally stopped in the absence of prolactin and GH.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Milk accumulation and secretion in the rabbit.
Over the 24 h period after suckling, total mammary-gland weight increased linearly indicating no reduction in the rate of milk secretion during the relatively long interval between sucklings in the rabbit. Thus, storage capacity is matched to the long storage period. Beyond 24 h in the absence of suckling at 24 h, the rate of milk accumulation declined rapidly. This decline was not prevented by the administration of ovine prolactin or by permitting suckling of sealed teats at 24 h. During the decline in secretory rate after 24 h, milk [Na] and [Cl] increased while [K] and [lactose] decreased, as in other species. It is concluded that the decrease in secretory rate after cessation of suckling is not caused by lack of hormonal stimulation; it is suggested that mammary distension caused by accumulation of milk is responsible.
Animals↗
Milk yield in rats in relation to activity and size of the mammary secretory cell population.
An attempt was made to partition changes in milk yield during lactation in the rat between changes in the size of the secretory cell population and changes in cellular activity. Groups of rats were studied on d 2, 7, 14, 21 and 28 of lactation. Milk yield increased between d 2 and 7, less markedly between d 7 and 14 and decreased between d 14 and 21. Milk secretion had apparently ceased on d 28. Total mammary DNA (DNAt) and RNA (RNAt) increased from d 2 to 14. It is concluded that of the increase in milk yield between d 2 and 14, an increase in cell population accounted for 75% and an increase in cellular activity for 25%. A decrease in activity appeared to be entirely responsible for the decrease in yield between d 14 and 21.
Animals↗
Mammary development and regression during lactation in goats in relation to milk secretion.
Mammary development was assessed in lactating goats using a combination of biopsy (for analysis of nucleic acids) and udder volumes (for determination of gross size). Single biopsies were shown to be highly representative of the composition of the whole gland provided that they were taken from carefully selected sites. Results indicated an increase in both milk yield and the size of the mammary cell population ( DNAt ) over the first three weeks of lactation. Yield, but not DNAt , continued to increase until peak lactation at around week eight. As milk yield fell between weeks eight and twenty-three the size of the cell population also decreased; beyond week twenty-three and until week thirty-six DNAt stabilized but yield continued to fall. It is concluded that the first part of the increase in milk yield during ascending (early) lactation in goats can be attributed to proliferation of secretory cells, but subsequently there is an increase in the amount produced by each cell. Likewise, declining lactation is initially characterized by a loss of cells, and yield per cell falls later.
Animals↗
Effects of prolactin, progesterone and ovariectomy on metabolic activities and insulin receptors in the mammary gland and adipose tissue during extended lactation in the rat.
Prolactin implants prevented the decline in milk yield and the resumption of oestrous cycles which occurred between days 22 and 28 in untreated lactating rats. Ovariectomy and progesterone implants only partially prevented the decline in milk yield despite preventing the occurrence of oestrous cycles. All three treatments increased total RNA content of the mammary gland compared with controls. In untreated rats there were no changes in mammary DNA content or the number of insulin receptors whereas lipoprotein lipase (LPL) activity decreased significantly during the declining phase of lactation. In contrast, the number of insulin receptors, LPL activity and glucose incorporation into lipid increased in adipose tissue. Prolactin prevented the increase in insulin receptors and lipid synthesis and significantly decreased LPL activity in adipose tissue. Progesterone stimulated LPL activity in the mammary gland and also prevented the increase in lipid synthesis and insulin receptors in adipose tissue but was without effect on LPL activity whereas ovariectomy stimulated LPL activity in the mammary gland but prevented only the increase in the number of insulin receptors in adipose tissue. The results show that raising the serum prolactin concentration can prevent the decline in milk yield during extended lactation and whilst part of this effect may be due to a direct effect on the mammary gland and an indirect effect due to inhibition of oestrous cycles, prolactin may also produce part of its effect on milk synthesis by inhibiting competitive metabolic processes in tissues such as adipose tissue.
Adipose Tissue↗
Stimulation of milk secretion with inhibition of milk ejection by corticosteroids during extended lactation in the rat.
Milk yield declined significantly between days 22 and 28 of lactation in rats, when lactation was extended by frequent replacement of older litters with younger ones. Corticosterone implants but not cortisol injections or implants prevented this decline. Cortisol, however, appeared to inhibit milk ejection since the mammary glands became engorged with milk and milk yield was improved dramatically by oxytocin injections. In both cases corticosteroid concentrations increased approximately threefold above basal concentrations. Both corticosteroids increased total mammary gland RNA content and lipoprotein lipase (LPL) activity of the mammary gland but were without effect on insulin binding. They also decreased LPL activity, lipogenesis and the number of insulin receptors on adipose tissue. Serum prolactin and insulin concentrations were unaffected by any of the treatments. The results suggest that corticosteroids inhibit milk ejection under certain conditions, may be circulating in lower concentrations, which thereby limit milk production, during prolonged lactation and may improve milk yield during extended lactation in part by suppressing anabolic activity in adipose tissue.
Adipose Tissue↗
Fetal imaging by nuclear magnetic resonance: a study in goats. Work in progress.
Nuclear magnetic resonance proton imaging was used to obtain images of goat fetuses in utero. The long T1 relaxation time of amniotic fluid makes it appear black on proton density images when examined using the Aberdeen imager, and so allows very good discrimination of the position and structure of the fetus. Some fetal internal tissues can be seen on T1 images. These findings suggest that NMR imaging has great potential in pregnancy studies.
Animals↗